Methods and apparatus for the manufacture of color cathode-ray tube screens

ABSTRACT

Methods for drying the upstanding walls of a cathode-ray tube faceplate, particularly around the area of the mask supporting studs are disclosed. The methods utilize an accurately controlled and automatically positionable head for removing excess liquid from the walls and stud area after a processing step. The liquid may be that remaining from either a prerinse in which case either forced air or a vacuum system may be utilized for the liquid removal; or after a developing step in the actual screen formation when a vacuum principle along is utilized for drying the wall area. The described apparatus for carrying out the method comprises a free-floating, self-orienting head which is pivoted to provide arcuate movement in a given substantially vertical plane, and reciprocatable shaft means connected to the free-floating head for indexing the head in a substantially perpendicular direction. Cam means associated with the reciprocatable movement causes engagement and disengagement of the head with the faceplate in accordance with the direction of movement thereof. The cam means causes the head to pivot in a substantially horizontal plane to bring the head into engagement with the faceplate wall.

Larson et a1.

[ 1 Feb. 1, 1972 METHODS AND APPARATUS FOR THE MANUFACTURE OF COLORCATHODE-RAY TUBE SCREENS John F. Larson, Seneca Falls, N.Y.; Walter A.Polaslienski, Roanoke, Va.

Inventors:

Sylvania Electric Products Inc.

Sept. 24, 1970 Assignee:

Filed:

Appl. No.:

Related U.S. Application Data Division of Ser. No. 723,098, Apr. 22,1968.

References Cited UNITED STATES PATENTS Primary ExaminerWalter A. ScheelAssistant Examiner-C. K. Moore Attorney-Norman .l. OMalley, Donald R.Castle and William H. McNeill [57] ABSTRACT Methods for drying theupstanding walls of a cathode-ray tube faceplate, particularly aroundthe area of the mask supporting studs are disclosed. The methods utilizean accurately controlled and automatically positionable head forremoving excess liquid from the walls and stud area after a processingstep. The liquid may be that remaining from either a prerinse in whichcase either forced air or a vacuum system may be utilized for the liquidremoval; or after a developing step in the actual screen formation whena vacuum principle along is utilized for drying the wall area. Thedescribed apparatus for carrying out the method comprises afree-floating, self-orienting head which is pivoted to provide arcuatemovement in a given substantially vertical plane, and reciprocatableshaft means connected to the free-floating head for indexing the head ina substantially perpendicular direction. Cam means associated with thereciprocatable movement causes engagement and disengagement of the headwith the faceplate in accordance with the direction of movement thereof.The cam means causes the head to pivot in a substantially horizontalplane to bring the head into engagement with the faceplate wall.

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ATTORNEY METHODS AND APPARATUS FOR THE MANUFACTURE OF COLOR CATHODE-RAYTUBE SCREENS CROSS-REFERENCE TO RELATED APPLICATION This application isa division of Ser. No. 723,098 filed Apr. 22, 1968 and assigned to theassignee of the present invention.

BACKGROUND OF THE INVENTION This invention relates to apparatus utilizedin the manufacture of color cathode-ray tube screens and moreparticularly to apparatus for removing excess liquid from the upstandingwalls and studs of a cathode-ray tube face plate after either a prerinseor developing step.

In the currently used methods of forming color cathode-ray tube screensof the shadow mask variety, a photographic deposition technique isutilized. This type of color tube has a screen formed of a set patternof triads of different color emissive phosphors. The colors generallyemitted are red, green and blue. The patterns are generally formed byapplying each color phosphor individually in the following steps:applying to the screen area of the face plate a photosensitized materialsuch, for example, as polyvinyl alcohol (PVA) sensitized with ammoniumdichromate. This photosensitized material may or may not have thephosphor particles dispersed therein. In either case, after thedeposition of the photosensitized material, the shadow mask structure,which comprises a thin apertured metal plate portion having one aperturefor each of the triads to be placed on the screen and which is usuallymounted on a heavier frame structure, is releasably mounted within theface plate portion by means of apertured springs attached to the shadowmask frame and fixed studs which are positioned on the upstanding faceplate wall and project inwardly thereof. After the mask is in position,the face plate-mask assembly is positioned on an exposure device and thecoated screen area is exposed to a suitable source of radiation, usuallyactinic, from a point source of light which is positioned tosubstantially duplicate the position of the electron gun to beassociated with that color in the finished tube. After exposure, whichcauses the exposed areas of the screens to become polymerized and thusinsoluble in a given solvent, the mask is removed from the face plateand the screen area is developed by washing the screen with a solventfor the unexposed areas remaining which removes them from the screen.When a PVA solution is used, the solvent is water.

The above steps are repeated twice more to complete the screen each timeusing a different phosphor and, during the exposure step, with thesource of exposure radiation in a different position corresponding tothe gun position to be utilized in the finished tube. For a moredetailed explanation of one particular method of screen deposition,reference may be made to U.S. Pat. No. 3,025,] 61. For a more detailedexplanation of the operation of a shadow-mask type of color cathoderaytube, reference is made to U.S. Pat. No. 2,986,080.

Because of the sequence of coating, exposing and developing necessary toform the screen and because of the fact that the developing is done withwater which is a solvent for the photosensitized PVA, it becomesnecessary to insure that the upstanding walls on the face plate aredried between each of the screen-forming operations since any waterremaining thereon would tend to cause dilution of the PVA being appliedfor the subsequent operation. Prior to applicants invention, this dryingwas usually accomplished either by an operator using a sponge or by ahand-held operator-controlled jet of high pressure air. Both of theseprior methods had disadvantages which adversely affected the quality ofthe finished tube. Namely, hand-wiping with a sponge clearly lacksuniformity of control. It was also possible for the operator, throughcarelessness, to inadvertently wipe away part of the previously formedscreen. Also, it was very difficult to dry the areas around the inwardlyprojecting studs, and water which often collected therearound sometimescaused sufl'lcient rust accumulation thereon to subsequently contaminatethe screen. Further, the sponge material would often tear off whenwiping the stud areas, and these particles remaining on or near thescreen could also cause contamination thereof.

The operator-controlled, hand-held high pressure air method of removalalso left much to be desired in that it too lacked uniformity of removaland, when being utilized on a partially patterned screen, it could causedamage to the pattern formed thereon.

OBJECTS AND SUMMARY OF THE INVENTION Therefore, it is an object of theinvention to obviate the disadvantages of the prior art methods.

Yet another object of the invention is to provide apparatus ideallysuited to carrying out the above cited objects.

Yet another object of the invention is to eliminate the inaccuracies andinconsistencies inherent in the prior art hand operated methods.

These objects are accomplished in one aspect of the invention by theprovision of apparatus for removing the excess liquid from the interiorupstanding walls of a cathode-ray tube face plate, the wall having agiven thickness and having inwardly projecting studs thereon, bycontacting the wall and the edge thereof formed by the thickness of thewall with an excess liquid removal system. The wall contacting portionof the system is formed to provide clearance over the inwardlyprojecting studs. While contact between the wall and the excess removalsystem is being maintained, relative movement is caused to occur betweenthe system and the face plate whereby excess liquid is removed and theupstanding wall and stud areas sufficiently dried before the nextoperation in the screen process takes place.

It will be seen from the above that this method of excess liquid removalobviates the disadvantages of the prior art and has many advantagesthereover. The excess removal system formed to contact the wall portioneliminates operator error and does not introduce possibly contaminatingsubstances into the screen area. Further, it is more accuratelycontrollable and thus precludes screen damage caused by operatorcarelessness.

Apparatus for carrying out the above methods comprises a face plate wallcontacting head which is formed to contact the edge of the wall formedby the thickness thereof and project inwardly of the wall a distance atleast sufficient to encompass the studs and being further formed toprovide clearance over the studs. The head is mounted at one end of afree-floating counterbalanced arm which is pivoted for arcuate movementabout a given axis at a point intermediate the head and thecounterbalance. The arm is mounted on a reciprocatable shaft havingmeans attached thereto for causing the desired reciprocation. Cam meansare provided, operative with the reciprocatable shaft for causing thehead to follow an arcuate path in a second direction to engage anddisengage from the wall in accordance with the direction of movement ofthe shaft. An excess liquid removal force supply, which may be eithervacuum or high pressure air, depending upon the condition of the facepanel at a particular stage of screening, is connected to the head. Alsoprovided are means for causing relative movement to occur between thehead and the face plate at least during engagement of the head with thewall.

This apparatus has many advantages over the previous hand-operationmethods and provides extremely accurate control over the excess liquidremoval operation. The freefloating head arrangement is ideally suitedto cooperate with the variable path traced by rotative movement of arectangular face plate and it also permits immediate self-orientationwith the wall of the face plate regardless of the angular orientation ofthe face plate when the excess removal system is energized. This featuremakes this apparatus ideally suited to performing its functions as asingle station on an automated or conveyorized screen applicationapparatus. However, it is to be noted that its use is not restrictedthereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of atypical color cathode-ray tube face plate;

FIG. 2 is a flow diagram of one embodiment of the invention;

FIG. 3 is a flow diagram of a second embodiment of the invention;

FIG. 4 is a diagrammatic representation of one means for causingrotation of the face plate;

FIG. 5 is an elevational view of one type of apparatus that may beutilized in carrying out the methods of the invention and is taken alongthe line 5-5 of FIG. 6;

FIG. 6 is a plan view of the apparatus and is taken along the line 6-6ofFIG. 5;

FIG. 7 is a sectional view of the wall contact head in its operativeposition with the wall of the face plate and is taken along the line 7-7of FIG. 6; and

FIG. 8 is a perspective view of the head in its entirety.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding ofthe present invention, together with other and further objects,advantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above describeddrawings.

Referring now to the drawings with greater particularity, there is shownin FIG. 1 a typical color cathode-ray tube face plate 10 having aconcave interior surface 11 on which the screen will be formed and anupstanding wall portion 12. The external edge of wall 12 has an edge 13formed by the thickness of the wall. The interior surface of wall 12 isprovided with at least two inwardly projecting, mask supporting studs14. It is the studs 14 which provide most of the difficulty in removingexcess liquid from the face plate.

Referring now to the flow diagram of FIG. 2, there are shown the basicsteps utilized in one embodiment of the invention. In this embodimentwhich might, for example, be a prerinse of the face plate prior toscreen deposition, the face plate 10 would be wetted with the rinsingmaterial and then positioned in a manner to facilitate drainage of theliquid. An exemplary position of the face plate could be with the planeof the face plate angled from the vertical at approximately Thisposition is a compromise well suited to cooperate with automaticmachinery; however, any orientation between 0 andl80 might also beappropriate depending upon circumstances. After a sufficient time toallow some natural drainage caused by the force of gravity, the wall ofthe face plate 10 and the edge 13 thereof formed by the thickness of thewall are contacted by an excess liquid removal system. The wallcontacting portion of this system is formed to project inwardly of thewall and provide clearance over the studs 14 positioned therein. Aftercontacting the wall 12 and edge 13 with the excess liquid removalsystem, an excess liquid removal force is supplied to the wallcontacting portion thereof and relative movement is caused to occurbetween the face plate and the system. When this embodiment is utilizedwith a prerinse cycle; that is, prior to any screen deposition, theexcess liquid removal force may be either a vacuum or a source of highpressure air.

The flow diagram of FIG. 3 illustrates an embodiment of a processwherein the invention is utilized during the actual screeningformations. In this instance, the interior surface of the face plate 11is coated with a pattern forming material such as PVA sensitized withammonium dichromate, and is then mated with an exposure negative whichis generally the shadow mask to be utilized in the finished tube. Themated face plate-negative assembly is then placed on an exposure deviceand exposed to a suitable source of point radiation as discussed above.After the exposure, the negative is removed from the face plate and theface plate is processed in the first developing sequence which compriseswashing the interior of the face plate with a solvent for the unexposedportions of the PVA. When PVA is the material being utilized, thesolvent is water. After developing, the face plate is again positionedin a manner to facilitate drainage and the wall 12 and edge 13 of theface plate 10 are dried in accordance with the last two steps of theembodiment described in FIG. 2. The only exception to this is that aftera partially patterned screen appears on the face plate, such as isillustrated in FIG. 7, the excess liquid removal force supply is bestrestricted to a vacuum removal system, since the application of highpressure air at this point may tend to destroy the previously formedpatterns. A suitable flow of air for a vacuum system would be oneutilizing a velocity of between 5075 ft./sec.

One means for accomplishing relative movement between the face plate 10and the excess liquid removal system is shown diagrammatically in FIG.4, wherein there is shown a suitable face plate-holding device which maybe a common vacuum chuck 30. This type of vacuum chuck is wellunderstood by those skilled in the art and needs no further explanation.The chuck 30 is connected to a rotatable shaft 32 which is journaled ina bushing 34 fixed in a gear housing 36. The end of shaft 32 remote fromchuck 30 is provided with a miter gear 38 which engages a mating mitergear 40 mounted on a second shaft 42. Shaft 42 is journaled by means ofbushing 44 in a second wall of gear housing 36 at one end thereof, andat its other end is journaled by means of a bushing 46 mounted in a wallof a second gear housing 48. This end of shaft 42 is also provided witha miter gear 50 which mates with miter gear 52 which is fixedly mountedon a third shaft 54; shaft 54 being journaled by means of a bushing 56in a second wall of housing 48. The end of shaft 54 remote from mitergear 52 is provided with a coupling portion 58 which is formed toprovide selective engagement and disengagement with a source of rotativepower. The source of rotative power 60 is shown in this instance ascomprising a motor 62 having a shaft 64 projecting therefrom and havingaffixed thereto a pulley 66. Pulley 66 is connected by means of a belt68 to a second pulley 70 mounted on the reciprocatable shaft 72 of afluid motor 74. A key 76 is provided on shaft 72 to cooperate with akeyway formed in pulley 70 so that shaft 72 may be reciprocatedtherethrough while still maintaining its ability to cause rotation ofshaft 72. Any suitable means may be provided for maintaining pulley 70in its properly aligned position, such, for example, as a bifurcatedU-shaped structure which engages the sides of pulley 70 and which isfastened to the supporting table. The external end of shaft 72 isprovided with coupling means 78 formed to cooperate and engage anddisengage from the coupling means 58 formed on shaft 54. Thus, to causerotative movement of the panel, fluid motor 74 is energized causingshaft 72 to extend and complete the coupling between coupling means 78and 58. Motor 62 is then energized which causes shaft 72 and coupledshaft 58 to rotate and, through the intermediary of miter gears 52 and50, shaft 42, miter gears 40 and 38, and shaft 32 provides the desiredrotative movement of the face plate. It will be obvious to those skilledin the art that this manner of obtaining rotation of the face plate isexemplary only and that certainly other apparatus may be utilized toachieve the same function. Further, it will also be obvious to thoseskilled in the art that it would be possible to maintain the face platestationary and revolve the excess liquid removal system therearound.

The apparatus for accomplishing the desired excess liquid removal isshown in FIG. 5 wherein there is provided a face plate wall contactinghead 80 to be more fully described hereinafter. Head 80 is mounted atone end of a free-floating counterbalanced arm 82 which is pivoted as at84 for arcuate movement about a given axis at a point intermediate head80 and the counterbalance weight 86. The arm 82 is supported by thepivot point, provided by bolt 87, and an arm-supporting beam 88 which issecured at its ends to a cylindrical sleeve 90 and at substantially thecenter thereof to the reciprocatable shaft 92 of a fluid motor 94. Thesecurernent of the supporting beam to the reciprocatable shaft 92 may beby any conventional means such as by welding or by a bolt 96 as is shownin FIG. 7. Sleeve 90 is coaxial with and slidably fits over a secondsleeve 98 which is coaxial with and surrounds shaft 92 to allowreciprocation of shaft 92 therein. Cam means 100 are provided forcausing the head 80 to follow an arcuate path in a second direction toengage and disengage from the wall of the face plate in accordance withthe direction of movement of the shaft and comprises a cam track 102formed in sleeve 98 and a cam follower 104 affixed to shaft 92 forcooperation with the cam track. The view of the apparatus in FIG. 5shows the head in its uppermost and disengaged position. This viewcorresponds to the phantomed position shown in FIG. 6 wherein the solidrepresentation of the head and arm structure is shown in its engagedposition.

In the particular embodiment shown, head 80 is disclosed as beingfixedly attached to the upper portion of a rigid tube 106 which isattached to arm 82 by means of clamps 108. A downwardly projectingportion of the rigid tube 106, designated 110, is connected to theexcess liquid removal force supply 112 by means of flexible tubing 114.The excess liquid removal force supply may either be a source of vacuumor a source of high pressure air, depending upon which of the methods ofthe invention described above are being utilized. A motor 116 is showndiagrammatically as being connected to force supply 112 to provide thenecessary power therefor.

Fluid motor 94 may be conventionally controlled as by means of atimer-actuated solenoid 118 which is actuated by standard timingequipment, not shown.

In operation, when fluid motor 94 is energized, shaft 92 begins movementin a downward direction carrying with it arm 82 which is afiixed to theend thereof, and, of course, head 80 which is mounted on the end of arm82. At the beginning of the downward cycle, the action of cam follower104 in cam track 102 is such as to cause shaft 92 and the associated arm82 to follow an arcuate path so that head 80 enters the interior of theface plate 10 at approximately the center thereof. As the shaft 92continues its downward movement, the head 80 contacts the wall 12 of theface plate and, by virtue of the counterbalanced action of the arm,remains in contact with the wall 12 while shaft 92 moves downwardly toits farthest limits. At this time, the rotation of the face plate 10 isbegun, as described by the apparatus shown in FIG. 3, and the rotationthereof is continued for a time sufficient to complete the liquidremoval operation. It will be seen that, while the face plate isrotating about a fixed center, the rectangular nature of the panel issuch that an imaginary line traced by the wall 12 thereof will be quiteirregular. However, the nature of the free-floating counterbalanced arm82 is such that head 80 remains in contact with the wall 12 regardlessof its angular orientation. Likewise, it is this free-floating action ofthe counterbalanced arm 82 which allows head 80 to make contact with thewall 12 regardless of the angular orientation of the face plate at thebeginning ofthe cycle.

It should be here noted that the drawings, for the sake of simplicity,have shown the apparatus and the face plate 10 in a substantiallyvertical position. As was pointed out above, this may or may not be themost suitable position for facilitating excess fluid drainage andtherefore, should the face plate 10 be mounted at some angle other thanzero from the vertical, the excess liquid removal system should bemounted at substantially the same angle so that the head 80 and the wall12 and the edge of the wall of the face plate 10 are substantiallyparallel in their contacting position.

After a sufficient number of revolutions of the face plate 10 to insureadequate removal of any excess liquidthis, of course, to be determinedby the airflow of the removal system and the speed and number ofrotations of the panelthe panel rotation is stopped and solenoid 118again actuated by the timing mechanism to start shaft 92 in its upwarddirection. This upward movement of shaft 92, of course, simply reversesthe downward process in that arm 82 and head 80 continue to rise untilhead 80 disengages in the vertical direction from the wall 12 of theface plate 10 and is then horizontally removed from the interior of theface plate 10 as cam follower 104 reaches the upper contoured portion ofcam track 102.

Referring now more particularly to head which is shown in greater detailin FIG. 7, the head comprises a body portion having a first steppedportion 122 formed thereon to remove excess liquid from the edge 13 ofthe face plate 10. A second stepped portion 124 is adjacent said firstportion and is formed to project inwardly of the wall 12 to removeexcess liquid from the interior surface of the wall over the distancefrom the edge of the wall to a point closely adjacent the stud 14. Athird stepped portion 126 is adjacent said second stepped portion and isformed to provide clearance over the stud 14. Aperture means 128 areformed in body portion 120 and interconnect the stepped portions withthe excess liquid removal force supply 112. A partically patternedscreen comprised of phosphor dots 129 is shown as being formed on theinterior surface 11 of face plate 10.

The external surfaces of body portion 120 which enclose and form theapertures 128 are formed to facilitate fluid flow therearound. Thisformation is shown more clearly in FIG. 8 wherein the facilitating meanscomprises angled walls 130 around stepped portion 126 and angled walls132 formed about stepped portion 124. These inwardly formed angles allowthe moisture remaining on the face plate wall portion to be drawn moreeasily into the aperture when vacuum is being applied since thesurrounding air is more readily drawn therethrough and helps to carrythe excess liquid away from the face plate.

Thus, it can be seen that there is herein provided methods and apparatushaving great advantages over the prior art hand methods. The control ofthe excess liquid removal is easily maintained and is consistentthroughout the entire operation, thus operator error is eliminated.Further, the invention is well suited to adaption as a stage in aconveyorized or automated processing setup.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

We claim:

1. An apparatus for removing excess liquid from the upstanding wall ofthe face plate of a cathode-ray tube, said wall having a given thicknessand having at least two inwardly projecting studs thereon, saidapparatus comprising: a face plate wall contacting head formed tocontact the edge of said wall formed by said given thickness thereof andproject inwardly of said wall a distance at least sufficient toencompass said studs and being further formed to provide clearance oversaid studs; a free-floating, counterbalanced arm mounting said head andbeing pivoted for arcuate movement about a given axis at a pointintermediate said head and said counterbalance; a reciprocatable shaftmounting said arm; means for causing reciprocation of said shaft; cammeans operative with said shaft for causing said head to follow apartially arcuate path to engage and disengage from said wall inaccordance with the direction of movement of said shaft; an excessliquid removal means; means interconnecting said removal means and saidhead; and means for causing relative movement to occur between said headand said face plate at least during engagement of said head with saidwall.

2. The apparatus of claim 1 wherein said means for causing reciprocationof said shaft is a fluid motor.

3. The apparatus of claim 1 wherein said cam means comprises asleevecoaxially aligned with and external of said shaft and having a cam trackformed therein and a cam follower affixed to said shaft and formed tocooperate with said track.

4. The apparatus of claim 1 wherein said excess liquid removal meanscomprises a vacuum system.

5. The apparatus of claim 1 wherein said means for causing said relativemovement between said head and said face plate comprises; means formounting said face plate for rotation about a given axis; means forcausing rotation of said face plate; means for intermittently engagingand disengaging said rotation causing means; and motor means forsupplying rotative power to said rotation causing means.

1. An apparatus for removing excess liquid from the upstanding wall ofthe face plate of a cathode-ray tube, said wall having a given thicknessand having at least two inwardly projecting studs thereon, saidapparatus comprising: a face plate wall contacting head formed tocontact the edge of said wall formed by said given thickness thereof andproject inwardly of said wall a distance at least sufficient toencompass said studs and being further formed to provide clearance oversaid studs; a free-floating, counterbalanced arm mounting said head andbeing pivoted for arcuate movement about a given axis at a pointintermediate said head and said counterbalance; a reciprocatable shaftmounting said arm; means for causing reciprocation of said shaft; cammeans operative with said shaft for causing said head to follow apartially arcuate path to engage and disengage from said wall inaccordance with the direction of movement of said shaft; an excessliquid removal means; means interconnecting said removal means and saidhead; and means for causing relative movement to occur between said headand said face plate at least during engagement of said head with saidwall.
 2. The apparatus of claim 1 wherein said means for causingreciprocation of said shaft is a fluid motor.
 3. The apparatus of claim1 wherein said cam means comprises a sleeve coaxially aligned with andexternal of said shaft and having a cam track formed therein and a camfollower affixed to said shaft and formed to cooperate with said track.4. The apparatus of claim 1 wherein said excess liquid removal meanscomprises a vacuum system.
 5. The apparatus of claim 1 wherein saidmeans for causing said relative movement between said head and said faceplate comprises; means for mounting said face plate for rotation about agiven axis; means for causing rotation of said face plate; means forintermittently engaging and disengaging said rotation causing means; andmotor means for supplying rotative power to said rotation causing means.